A runic knot is a type of complex interlacing ornament, which can be found in Romanesque design, but it is mostly associated with Anglo-Saxon and Celtic work, where it is often used in high crosses.
The definition of "runic knot" can be found here:
Bibliography:
James Stevens Curl. "runic knot." A Dictionary of Architecture and Landscape Architecture. 2000. Encyclopedia.com. Web.12 Jan. 2014. <http://www.encyclopedia.com>.